Erm. Mine is probably Rinaldo, Peru international. I was in Ligue 2 in France and never had I seen anybody tear up a lower league like he did, didn't need any really complex role, Centre Midfield- Attack and bang, 24 assists, 7 goals and an average rating 7.8 ish. That save is now in 2019, and I'm not on FM now but I shall have to try and see if he took up a non playing role
Alejandro Rocamora. Not the biggest player I've ever signed, but by far the most succesful one.
Beside Roca, it must be Marian Kelemen. Signed him as a backup for Julio Cesar, but when Julio Cesar got injured (4 months :s) Kelemen took over, and did brilliant. Sold him to Manchester United for 6 - 7 millions after that